how can i find out how much someone is paying for ppc?

I need to find out or estimate how much a site is paying for ppc daily.
I have tried google traffic estimator and it says it's $15 per click, but that sounds too high to me. the keyword is something that someone would type if they were looking for an attorney with a particular specialization + city.
Anyway, how do I find out what a typical site whose advertisements come up for this keyword is paying daily?

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